1. Field of the Invention
This invention relates to a fixing method and device in which a high-frequency wave such as microwave is applied to fix an unfixed image such as a toner image on an image bearing member such as plain paper to thereby form an image thereon, and more particularly to a fixing method and device for heating by electromagnetic wave image bearing members of various width sizes bearing an unfixed image thereon while conveying such image bearing members.
2. Description of the Prior Art
In image formation apparatus wherein a developed image formed on an image bearing member by an image formation method such as electrophotographic method is transferred onto an image bearing member such as plain paper and the transferred image is heated and fixed to provide a fixed image, there has heretofore been proposed a system for fixing unfixed image by microwave heating.
Such heating-fixing method using a high-frequency wave such as microwave and a device therefor have already been disclosed in Japanese Patent Publication No. 38171/1974, Japanese Laid-open Patent Application No. 20039/1977 and Japanese Patent Publication No. 10865/1979. This high-frequency wave heating-fixing device is an excellent one which has eliminated the following disadvantages in the so-called extraneous heating and fixation. That is, it is a compact device which reduces the wait time until a temperature necessary for fixation is reached, which eliminates the danger of a fire or the like occurring when a recording medium such as paper stays within the fixing area by some cause or other, and which prevents creation of wrinkles and disturbance of image which would otherwise result from the contact of the recording medium with a heating roller or the like.
However, a device which can provide a uniform and good heating-fixing effect without requiring cumbersome adjustments where the width sizes of unfixed image bearing members are various is not yet known. In the prior art system, when the fixing device is constructed so as to conform to the fixation of an image bearing member of a maximum width size, excessive fixation may occur in the case of image bearing members of small sizes, that is, developer may become excessively fluidized to disturb the image or the image bearing members may become too dry and degenerated or sometimes scorched. On the other hand, when the fixing device is constructed so as to conform to a maximum size, unsatisfactory fixation may occur in the case of image bearing members of large sizes and fixativeness may be lost.
However, the width dimension of the image bearing member having thereon an unfixed image to be fixed is not constant but various. Therefore, in the case of fixation of an image bearing member of a small width dimension, wasteful high-frequency wave energy which does not contribute to fixation would be put out and this is not preferable in terms of energy saving. Also, no recording medium is present in the portion which does not contribute to fixation, so that the neighborhood of the fixing device is heated by leakage high-frequency wave to thereby increase the ambient temperature, and this is not preferable in terms of the rise of the temperature within the apparatus.